Connected: An Internet Encyclopedia
RFC 1812 - E.3.2 The Variant Router Requirements Algorithm

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### E.3.2 The Variant Router Requirements Algorithm

Some Router Requirements Working Group members have proposed a slight variant of the algorithm described in the Section [5.2.4.3]. In this variant, matching the type of service requested is considered to be more important, rather than less important, than matching as much of the destination address as possible. For example, this algorithm would prefer a default route that had the correct type of service over a network route that had the default type of service, whereas the algorithm in [5.2.4.3] would make the opposite choice.

The steps of the algorithm are:

1. Basic match
2. Weak TOS
3. Longest match
4. Best metric
5. Policy

Debate between the proponents of this algorithm and the regular Router Requirements Algorithm suggests that each side can show cases where its algorithm leads to simpler, more intuitive routing than the other's algorithm does. This variant has the same set of advantages and disadvantages that the algorithm specified in [5.2.4.3] does, except that pruning on Weak TOS before pruning on Longest Match makes this algorithm less compatible with OSPF and Integrated IS-IS than the standard Router Requirements Algorithm.

Next: E.3.3 The OSPF Algorithm

Connected: An Internet Encyclopedia
RFC 1812 - E.3.2 The Variant Router Requirements Algorithm